In the context of applications in the field of toll fee collection for lorries and check-in systems at toll plazas, very accurate and efficient weighing systems for lorries are used in order to be able to impose charges based on vehicle weight. In this process it is desirable that measuring can take place in moving traffic, without stopping the traffic. Weight measuring is then used to calculate the charge (toll charge).
At present three technical solutions for weight acquisition are known, namely static weighbridges, low-speed axle load scales, and high-speed WIM (weigh-in-motion) systems.
Weighbridges are static measuring systems. In order to weigh a lorry, it needs to drive onto the weighing pad, stop thereon, and wait for the display to stabilise. While the process is very accurate, it is, however, unfortunately also very time-consuming and not suitable for weighing in moving traffic.
Low-speed axle load scales are short weighbridges, about one meter in length, that can efficiently and accurately measure an axle load if a vehicle moves over said scales steadily and slowly. These scales are associated with disadvantages, on the one hand as a result of expensive installation because a large pit has to be dug and secured, which involves closure of a lane for several days, and on the other hand as a result of the very significant expenditure arising from intensive maintenance. Furthermore, the speed range of lorries passing over such scales is limited to approximately 10 to a maximum of 30 km/h.
High-speed WIM (weigh-in-motion) systems comprise small rail-like sensors, as known from U.S. Pat. No. 5,461,924, which is hereby incorporated herein for all purposes by this reference. These sorts of WIM sensors are quickly and easily installed in the roadway. The WIM sensors are installed in a small groove with maximum dimensions of 60×70 mm and are sealed in the roadway. Closure of the lane takes place for less than 8 hours. These systems are also maintenance-free and are successfully used in the area of high-speed WIM, where vehicles normally move at highway or motorway speeds. However, when passing at low speeds, in particular at irregular speeds, when accelerating, when decelerating during passing, and in stop-and-go traffic the accuracy of weight measuring is no longer maintained; substantial measuring errors occur. In these applications such systems cannot successfully be used.
U.S. Pat. No. 6,459,050, which is hereby incorporated herein for all purposes by this reference, proposes a method for improving readings that were carried out with a static weighing system, wherein the vehicles are to be weighed while travelling at a speed of approximately 16 km/h. The speed of vehicles when passing over the scales represents a big problem, because at high speeds the vehicles remain only a short time on the scales, and conventional weighing systems are only approximately 60 cm wide. Vehicle oscillations when passing over the scales result in substantial inaccuracies because the vehicles remain on the weighing system only for a few milliseconds. Furthermore, the sensitivity of the weighing system is not constant along the entire passing length, which again reduces the measuring accuracy. While in the case of very short weighing systems a constant speed can be assumed, in the above-mentioned printed publication for these reasons it is proposed that the measured weights be multiplied by the actually-measured speeds, and the product be integrated over that time. In this manner the errors are corrected. However, care must be taken in these systems that the length of the weighing system is always sufficiently long. Instead of the passing length of 60 cm of known weighing systems it is proposed that the length be such that in each case at least two axles of a vehicle can be situated on the weighing system at the same time. Such systems are very complex to install and very expensive.